Flame retardant thermoplastic resins have been widely used, particularly in the electric and electronic packaging industry. For many applications, a plastic is deemed acceptable for use as part of a device or appliance with respect to its flammability if it achieves a UL 94 (Underwriters Laboratory®) flammability test rating of V-0 for stock shape products (sheet, rod, tube and film) or VTM-0 for thin materials. Briefly, a UL 94 Flammability Rating of V-0 means that using a vertical burn test, burning stops within 10 seconds after two applications of ten seconds each of a flame to a test bar. No flaming drips are allowed. Traditionally, halogenated compounds have been employed as flame retardants in combination with one or more synergists to achieve high levels of safety against flames (flame retardancy). Halogen based compounds are very effective in imparting flame retardancy, especially when used in combination with a synergist such as antimony oxide. With such combinations, a relatively low amount of flame retardant is required to achieve the desired V-0 rating.
Several types of processes are known for preparing halogenated flame retardants. Most of these materials are immiscible to polymers. Thus, multiphase systems are formed which result in a resin that is non-transparent. If the preparation involves orientation, cavitations during the stretching process render the material even more non-transparent. Recently, several melt extrudable flame retardants have become commercially available. Such flame retardants include brominated polystyrene, among others. However, most of these flame retardants are not very heat stable, especially at high processing temperatures. For example, decomposition of flame retardant halogenated polyester produces free halogen gas and/or halogen compounds which are extremely harmful to the process equipment as well as the environment. These compounds may corrode dies, extruders, and other metallic parts. In recent years, there has been a movement to completely regulate the use of halogenated material due to overall environmental concerns. This is especially true in Europe and Japan.
By using special catalysts during polymerization, polyethyleneterephthalate (PET) can be prepared to attain a moderate flame retardancy of V-2. To obtain a V-0 rating, various flame retardants must be compounded into the PET. For thin film, a VTM-2 rating can be obtained when the film is thick enough (with thickness of about 2 to about 20 mil typically required) and/or when the molecular weight of the PET is high enough. U.S. Pat. No. 6,136,892 to Yamauchi et al., discloses thermoplastic resin compositions, including PET and its copolyester, having red phosphorus to obtain the desired flame retardancy. However, U.S. Pat. No. 6,136,892 is directed to injection molding applications only wherein the part is thick and not oriented, such as for mechanical parts, electric and electronic parts, automobile parts, and housings and other parts of office automation apparatuses and household electric appliances, thereby limiting its usefulness.
U.S. Pat. No. 4,042,561 to DeEdwardo et al. discloses flame retardant compositions containing polyphosphazenes blended in resins including polyester, polyamide, and polycarbonate resins. The polyphosphazenes taught in U.S. Pat. No. 4,042,561 are halogenated.
U.S. Pat. No. 4,104,259 to Kato et al. discloses fireproof polyesters comprising linear aromatic copolyester with flame retardant elements in the polyester backbone. The copolyester is prepared from brominated dihydroxy alkoxy-diphenyl sulfones. The addition of an organic penta-valent phosphorus compound is needed in many cases to impart the desired fireproof properties to products prepared from the polyesters.
U.S. Pat. No. 4,517,355 to Mercati et al. discloses a linear flame retardant copolyester resin containing phosphorus in the polymer backbone.
U.S. Pat. No. 5,650,531 to Chang et al. and U.S. Pat. No. 4,157,436 to Endo et al. disclose the use of flame retardant phosphorus-containing polyester oligomer and polymer resin having pendant phosphorus containing groups. U.S. Pat. Nos. 5,650,531 and 4,157,436 teach the polyester having a greater heat-stability as compared to polyester having phosphorus in the backbone. Additionally, WO02066538A1 discloses a polyester film having phosphorus-containing flame retardant copolyester wherein the phosphorus atoms are present in the side chain.
U.S. Patent Application 2001-0018476 and U.S. Patent Application 2001-0029274 disclose low flammability and UV resistant oriented polyester film. The flame retardant disclosed is an organic phosphorous compound, dimethyl methylphosphate, incorporated into the film by means of masterbatch. However, a large amount of flame retardant is needed to obtain the desired flame retardant properties. Additionally, since the flame retardant is susceptible to hydrolysis, hydrolysis stabilizers are generally used.
The tendency for most thermoplastic resins to burn is one problem in the art. Further, under intensive heat, burning plastics also melt and decompose. The resultant burning polymer drips, thereby causing additional problems. Therefore, the UL-94 standard includes dripping criteria. In order to achieve a UL-94 V-0 (or VTM-0) rating, there cannot be dripping that causes cotton positioned 300 millimeters below the test subject to be ignited by flaming particles or drops. Although in most halogenated flame retardant systems, anti-dripping particles are not required, with phosphorous based flame retardants, anti-dripping particles are generally needed. For most molding applications, a fluorinated polyolefin has been traditionally used to prevent dripping. In addition, grafting or cross-lining agents have been used for this purpose.
Talc and other layered inorganic materials have been used in the plastics industry due to the ability of these materials to increase dimensional stability, flexural modulus, and impart improved heat distortion temperature. For polypropylene film, these materials have been used as anti-blocking or nucleation agents. Talc has also been combined with polyurethane to facilitate crystallization of a polyurethane composition, particularly a polyester-based polyurethane composition (see U.S. Pat. No. 6,458,880). The addition of talc can enable rapid formation of products by, for example, injection molding, compression molding, extrusion, and film formation techniques. U.S. Pat. No. 6,174,943 discloses a flame retarding polycarbonate composition having an organo-phosphorous material. In U.S. Pat. No. 6,174,943, talc is used as an effective material for preventing dripping of the molded articles.
The disclosures of the foregoing are incorporated herein by reference in their entireties.